Illumination unit for the generation of optical sectional images in transparent media, in particular in the eye

ABSTRACT

Illumination unit for the generation of optical sectional images in transparent media, particularly in the eye is disclosed. In the arrangement according to the invention, the low-divergence beams emitted by a laser serving as illumination source are imaged on or in the eye under examination by a reflection element which is controllable in a defined manner and beam deflection elements present in the beam path. The optical sectional images resulting in and on the eye can be observed and/or recorded, further processed and evaluated with an image processing unit in a known manner. In the solution according to the invention, a sectional image is generated by the deliberate periodic beam deflection of a particularly fine laser beam with high depth of focus, which sectional image remains sharp through the entire dimension of the object to be examined and makes possible an improved evaluation. The intensity of the laser beam bundle can be varied in such a way that it is sufficient for observation and documentation, but so that the diameter of the beam bundle is fine enough for a high detail resolution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of PCT Application Serial No.PCT/EP02/12561, filed Nov. 11, 2002 and German Application No. 101 55464.8, filed Nov. 12, 2001, the complete disclosures of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention is directed to a special illumination unit forgenerating a variable slit image such as is used in ophthalmologicalexamination instruments, including slit lamps. A light section isgenerated by slit image projection in the more or less transparentobject under examination, e.g., in the interior of the eye. Theparameters of the section bundle are variable, particularly the angle ofincidence, the dimensions of the slit image, its intensity and thespectral composition. Information about the object under examination canbe acquired from the shape, position and intensity of the scatteredlight of the sectional image generated in this way.

b) Description of the Related Art

In slit lamps such as those described in Rassow, B. et al.,“Ophthalmologic-optical instruments”, 1987, Ferdinand Enke VerlagStuttgart, pages 99ff and 137ff, mechanical/optical elements such asslit diaphragms have been used up until now to generate slit imaging.The variable, smallest possible slit widths which are required for highoptical detail resolution within the optical section are very difficultto achieve. Further, the mechanical component groups are very cumbersometo adjust, and this is made even more difficult by the thermal expansionof the component groups, among other things. Reproducibility ofadjustments for measurement purposes is possible only to a limitedextent. The multiplicity of possible illuminated field geometries isextremely limited by the fixed slit diaphragms and pinhole diaphragmsand the space required by the latter.

Since slit image projection involves optical imaging with a physicallydefined depth of focus, the imaging must always be focused strictly onthe point of examination. A section bundle which is focused over theentire extension of the human eye can not be achieved with the solutionsmentioned above. While conditions can be improved with an arrangementbased on the Scheimpflug principle, the technical expenditure iscorrespondingly greater.

DE 198 12 050 A1 describes a method and an arrangement for illuminationin an ocular microscope. A wide variety of illuminating mark geometriesis generated by means of opto-electronic components. The illuminatedfield geometries are projected on the anterior portion and fundus of theeye and are used for general examination of the eye.

Methods and arrangements for illuminating the anterior segments of theeye in which a planar configured laser is used as light source aredescribed in U.S. Pat. Nos. 5,404,884, 5,139,022 and 6,275,718. However,in these solutions the limited variability of the slit dimensions, theutilized wavelength of the laser sources, and the lack of a possibilityfor generating multiple-slit projections are disadvantageous undercertain circumstances. The described arrangements are not slit lampdevices used in normal diagnostic operation. Further, the system forreceiving the scattered light from the eye has a physically limiteddepth of focus which can not completely acquire the expansion area ofthe sharp sectional laser image.

OBJECT AND SUMMARY OF THE INVENTION

It is the primary object of the present invention to further develop theknown solutions in such a way that a sufficient light intensity forobservation and documentation, particularly with analog or digital imageacquisition technology, can be ensured in spite of the smallest possibleslit width and greatest possible depth of focus which are required forhigh optical detail resolution within the optical section.

According to the invention, this object is met by an illumination forgenerating optical sectional images in transparent media, particularlyin the eye, comprising a laser which is provided as illumination sourceand a reflection element which is controllable in a defined manner forthe deliberate deflection of the laser beams.

With the proposed solution for an illumination unit for generatingoptical sectional images in the eye, a sectional image is generated bythe deliberate periodic beam deflection of a particularly fine laserbeam with high depth of focus, which sectional image remains sharpthrough the entire dimension of the object to be examined and makespossible an improved evaluation. The intensity of the laser beam bundlecan be varied in such a way that it is sufficient for observation anddocumentation, but so that the diameter of the beam bundle is fineenough for a high detail resolution. The proposed illumination unitcould be constructed in such a way that it is used in addition to anexisting illumination unit of an ophthalmological instrument such as aslit lamp. As an add-on module for existing ophthalmologicalinstruments, it could substantially simplify examinations of the humaneye through broad application and improve the accuracy of theexamination results.

The invention will be described in more detail in the following withreference to an embodiment example.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic view of a slit lamp with the illumination unitaccording to the invention; and

FIG. 2 is a schematic view of a microscanner mirror.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the construction of a slit lamp with the illumination unit,according to the invention, for generating optical sectional images. Thelow-divergence beams proceeding from the laser serving as illuminationsource 1 are imaged on or in the eye 6 under examination by a reflectionelement 4 which is controllable in a defined manner and beam-shaping andbeam-deflection elements (shown schematically) in the beam path. Theangle and the direction of the laser beam 3 directed onto the eye underexamination are freely selectable.

A laser diode module, for example, is used as illumination source,preferably in the blue or green spectral range. Illumination with lightin the green or blue spectral range results in higher scattering in thetransparent media of the eye, which leads to clearer sectional imagesfor optical diagnosis. A very fine, low-divergence laser beam 3 isgenerated by means of focusing optics 2. This laser beam 3 impinges at adetermined angle and distance on the reflection element 4 whosefrequency and amplitude can be controlled by the control unit 7. Thereflection element 4 is a mirror which has small dimensions and which istiltable in two or more directions independent from one another. Thisso-called microscanner mirror chip preferably belongs to the group ofMEMS (microelectro-mechanical systems) and can be constructed in anymanner desired. A chip of this type is available, for example, fromFraunhofer-Institut für Mikroelektronische Schaltungen und SystemeDresden under the trade name “Resonanter 1D- und2D-Mikroscannerspiegel”.

Also, a DMD (digital mirror device) type microscanner mirror chip suchas that available from Texas Instruments, for example, can be used as areflection element.

FIG. 2 shows a schematic view of a MEMS type microscanner mirror chip.The actual mirror element 9 is tiltable along axes 11 and 12 by means ofthe holder frame 10. Tilting around the respective axes 11 and 12 can becarried out, for example, by generating harmonic mechanical oscillationsof suitable frequency and amplitude by means of electrostatic control.The microscanner mirror, which is fastened by torsion springs or by auniversal joint suspension, is accordingly set in harmonic mechanicaloscillations. In this way, many different shapes can be imaged on or inthe eye under examination from the punctiform low-divergence laser beam3. When the microscanner mirror oscillates in only one direction, forexample, the image of a slit is generated.

In the microscanner mirror chip produced by Fraunhofer-Institut, theadjustable oscillation frequencies are between 150 Hz and 20 kHzdepending on the image to be produced. The amplitude of the oscillationis directly proportional to the drive voltage in this microscannermirror chip and can be regulated by means of this drive voltage.Deflecting angles of up to 60° can be achieved by the electrostaticdrive principle.

In principle, electrostatic, thermomechanical, piezoelectric andmagnetic excitation forms are possible for the control of themicroscanner minors. A large number of displayable images, e.g., singleslits and multiple slits, grids and rasters, result from the manypossibilities of modulation with respect to frequency, amplitude andintensity.

A particular advantage of the illumination unit according to theinvention consists in the possibility of a quasi-simultaneous imaging ofa plurality of slit images on or in the eye under examination. In thisway, the examination period can be shortened and the physical stress onthe patient can be substantially reduced.

The laser beam 3 which can be changed in this way with respect to itspropagation direction and also with respect to its intensity byadditional modulation is deflected on or in the eye 6 under examinationby the beam-shaping and beam-deflecting element 5.

The optical sectional images resulting in the eye 6 can be observed inthe usual manner, e.g., with a variable-magnification stereo microscopeor similar arrangement. Current ophthalmological instruments generallyhave, in addition to an observation system, an image processing unit bymeans of which the sectional images can be recorded, further processedand evaluated.

Because of its small dimensions, the illumination system according tothe invention can be integrated in many different ophthalmologicalexamination instruments, especially slit lamps. The illumination unitcan be combined with the conventional, existing illumination arrangementor can be used separately. It is also possible to use the illuminationunit as an add-on module for expanding existing ophthalmologicalinstruments in order to substantially simplify examinations of the humaneye and to improve the accuracy of the examination results. Modernophthalmological examination instruments have additional documentationdevices such as photo/video components for analog and digital imagerecording and image processing and an automatic image evaluation forobtaining measurement values of the object under examination. In orderto increase the depth of focus during documentation, the recording unitwith its receiver (e.g., CCD chip) can be inclined relative to theoptical axis so as to be adapted to the angle of the slit inputradiation direction corresponding to the Scheimpflug condition. Theeffect can be monitored with a monitor image in an advantageous manner.

In the illumination unit according to the invention, the intensity ofthe laser source can advantageously be selected in such a way that it issufficient for observation and documentation, but such that the diameterof the beam bundle is fine enough for a high detail resolution andlimiting values for the spectral irradiation strength on the fundus ofthe eye are not exceeded. Further advantageous effects, e.g., spatialseparation of projection structures, can be achieved by means of asuitable modulation of the intensity of the light source. For thispurpose, current laser diode modules generally have an additionalconnection for applying a modulation signal. Different illuminationstructures such as point grids and line grids or multiple-slit imagescan be realized in this way. These illumination structures can likewisebe generated as dynamic processes in order to automate certain sequencesor processes.

The described illumination unit serves to generate optical sectionalimages not only in the eye but also in different transparent media. Theillumination unit can also be used, for example, for examination ofliquid layers and/or for testing optical components such as lenses,prisms, and so on. It can be advantageous that the microscanner mirroris not set in oscillations but rather executes a slow scanning movementover the object to be tested. Since not all microscanner mirrors offerthe possibility for a control of this kind, an appropriate model must beselected.

While the foregoing description and drawings represent the presentinvention, it will be obvious to those skilled in the art that variouschanges may be made therein without departing from the true spirit andscope of the present invention.

1. An slit lamp comprising: a laser being provided as an illuminationsource; and one reflection element that, during use of the illuminationunit, is controllable by a drive voltage in a defined manner for thedeliberate deflection of the laser beam and is tiltable about two axesindependent from one another; wherein the one reflection element iscontrolled such that an amplitude of an oscillation of the onereflection element is proportional to the drive voltage, and thedeliberate deflection generates optical sectional images in transparentmedia; and wherein each of the two independent axes, about which thereflection element is tiltable, is arranged to always intersect bothwith an upstream beam path and with a downstream beam path of the laserbeam which is deflected by the reflection element.
 2. The slit lampaccording to claim 1; wherein the beam emitted by the laser serving asillumination source has a low divergence; and/or wherein the beamemitted by the laser is in the blue or green spectral region; and/orwherein the intensity of the illumination unit is controllable; and/orwherein the illumination unit has beam-shaping elements.
 3. The slitlamp according to claim 1; wherein the illumination source is a laserdiode module.
 4. The slit lamp according to claim 1; wherein anoscillation frequency and the amplitude of the oscillation of thereflection element are controllable; wherein the reflection element is amirror of small dimensions; and wherein the reflection element is amicroscanner mirror chip of any type of construction.
 5. Anophthalmological examination instrument; wherein it contains an slitlamp according to claim 1; wherein the illumination unit is used incombination with a conventional illumination device and can be switchedon when needed, or wherein the illumination unit is used separately fromthe conventional illumination device and can be added optionally;wherein additional documentation devices are provided; wherein there isan additional automatic image evaluation for obtaining measurementvalues of the object under examination; and wherein the documentationdevice can be tilted at an angle for increasing the depth of focusaccording to the Scheimpflug condition so as to improve acquisition ofthe spatial extent of the sectional image through its entire dimension.